Will the Rain Gods smile on India during its battle with Covid19?
In an otherwise gloomy and uncertain scenario, one segment of the economy has been holding the fort – agriculture and allied industries. Being predominantly monsoon-dependent, the agriculture sector, and the economy at large, have been crossing their fingers that Indian monsoon 2020 does its bit to keep this sector strong.
The good news is that after clocking the highest monsoon rainfall in the last 25 years during 2019, the IMD has predicted that India is likely to have a normal monsoon again this year!
The good news doesn’t end there; according to the Met Department’s second forecast, the rainfall is expected to be more or less normal, all across the country. Even the monthly distribution of rainfall seems to be promising, with 103% of the Long Period Average (LPA) in July and 97% in August.
What’s behind this positive prediction?
This year, the trio of oceanic parameters – El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Madden Julian Oscillation (MJO) – seem all set to favourably influence Indian monsoon 2020. These terms may sound highly complex but we’ll break them down a little to bring out why they are so relevant and what they portend for Indian monsoon 2020.
Taking stock of tailwinds
El Niño–Southern Oscillation (ENSO)
The ENSO cycle is simply a scientific term that describes the fluctuations in temperature between the ocean and atmosphere, in the east-central Equatorial Pacific. Why is it relevant? Because global weather and climate are impacted by these deviations. When this temperature is relatively warm, it is called El Niño and when it is relatively cool, it is referred to as La Niña. El Niño and La Niña episodes typically last for 9 to 12 months but some prolonged events may last for years.
Impact on Indian Monsoons
In general, an El Niño event during winter results in warm conditions in the Indian subcontinent and this dry weather, in turn, results in a deficient monsoon. Incidentally, it could also lead to drought in far-away Australia. On the other hand, La Niña results in better monsoons in India.
In the recent past, India experienced deficient rainfall during El Niño years 2002 and 2009; but then again, the monsoon was normal during El Niño years of 1994 and 1997.
Where the La Nina is concerned, India experienced very good rains during La Niña years of 1990, 1995, 1998, 2007, and 2011. The only time there was a strong La Niña year that coincided with a weak Indian monsoon was in 1999.
So, without mincing words, the ENSO is an important factor but it doesn’t dictate the ultimate fate of the Indian monsoon alone; being the complicated phenomenon that weather is, there are other factors too.
That being said, this year, a weak En Niña is expected, which theoretically indicates a good monsoon for India.
Indian Ocean Dipole (IOD)
The Indian Ocean Dipole (IOD) is defined by the difference in the sea surface temperature between the two equatorial areas of the Indian Ocean – a western pole near the Arabian Sea (in western Indian Ocean) and an eastern pole closer to the Bay of Bengal (in eastern Indian Ocean). The IOD affects the climate of Southeast Asia, Australia and other countries that surround the Indian Ocean Basin. The Indian Monsoon is invariably influenced by the IOD.
If the sea surface temperature of the western end rises above normal (0.4°C) and becomes warmer than the eastern end, it leads to a positive IOD. This condition is favourable for the Indian Monsoon as it causes a kind of barrier in the eastern Indian Ocean and all the southwesterly winds blow towards the Indian sub-continent.
Last year, despite fears that the El Niño conditions in the Pacific Ocean, a positive IOD, with some help of other weather phenomenon, saved India from what could have been a bad monsoon. In fact, it delivered record rains!
This year, according to Australian Met (BOM) and several agencies, the hero of Indian monsoon 2019, the IOD, is likely to remain ‘neutral’ during this South west monsoon season. By itself, that’s good for Indian monsoon 2020.
When Weak La Niña meets Neutral IOD…
Now that we are aware of these two climate giants, who clash or collude to give India a bad or good monsoon, let’s take a look at how the monsoon has panned out in the past, when a weak La Niña meets a Neutral IOD.
Since 1989, whenever a weak La Niña weather pattern has formed and the IOD index is neutral Indian monsoons have been more or less normal (i.e., normal means 96-104% of the LPA).
But coming back to Indian monsoon 2020, the IMD, in a report on 1st June 2020, stated that currently, ENSO-neutral conditions are prevailing over the equatorial Pacific and neutral IOD conditions are prevailing over the Indian Ocean. Global models indicate cool ENSO conditions are likely to prevail during the monsoon season, with some possibility of development of weak La Niña conditions in the later part of the monsoon season. If these patterns do not change, we expect Indian monsoon 2020 to be ‘Normal’ (Rainfall 95% to 99%).
Is there a chance that these predictions can get thrown out?
It’s the weather we’re talking about. Without disrespect to any weather bureau anywhere in the world, there’s a reason why the phrase ‘Unpredictable as weather’ emerged!
There were concerns amongst weather-watching communities that the powerful Nisagara could slow the progress of Indian monsoon 2020 to other parts of the country and lead to a significant rainfall deficit in June. According to these experts, we could witness a repetition of the situation in 2019, wherein Cyclone Vayu stopped the progress of the monsoon during the second week of June, after its onset over Kerala on June 8. In June 2019, India witnessed a 33% deficit in rainfall; fortunately, however, the overall accumulation in monsoon 2019 was 10% excess.
There is one more concern, in the form of the lesser-known and highly unpredictable Madden Julian Oscillation (MJO), which can have a dramatic impact on the tropics during the monsoon season.
Madden Julian Oscillation (MJO)
While the ENSO and IOD are stationary, the MJO is a transient disturbance of cloud, rainfall, wind and pressure, traversing nearly along the equator in the tropics. An average cycle of the MJO could last from 30-60 days, while the El Nino and IOD may last for several seasons. However, the MJO could visit a single region multiple times over during a single season.
The MJO is an intra-seasonal oceanic index which has two phases: Active Phase (enhanced rainfall) and Suppressed Phase (decreased rainfall). The amplitude of MJO is another factor of concern and is rather tricky to predict.
The MJO can modify, retard or accelerate the timing of a monsoon and its strength. It can alter the intensity and frequency of extreme events like drought, flood, ‘break monsoon’ and heat wave, etc. It could also produce rains similar to the El Nino/ La Nina and IOD but because of its transient duration, its impact appears in weekly averages. This may get diluted in the monthly or seasonal projections. However, monitoring and assessing the strength of MJO for real-time impact remains a challenge.
As things stand, Skymet has predicted that the MJO will remain in phase-1 with a moderate amplitude to support the sustenance of a cyclone through its travel to the Konkan region. The favorable position of the MJO will last till the end of the June.
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